Add AWS::SNS::Message and build-in authenticity-checking.

AWS::SNS::Message#authentic? will return true if the message is cryptographically authenticated
(see http://docs.amazonwebservices.com/sns/latest/gsg/SendMessageToHttp.verify.signature.html).
To-do:
* support subscription-confirmation and unsubscribe messages; this just supports
notifications.  Should just mean changes to canonical_string method.
* decide whether it's really OK to return false in the event of the check throwing an error (for
example, if the cert-download fails too often or times out).  Might be best to leave that up to
the caller?
Add support for Message finding out its own origin.

Introduce the concept of a message's origin, and introduce a partial implementation of
an AutoScaling originator (partial, in that there's not coverage for all of the data that
auto-scaling will include in the SNS' body).

The origin-selection currently works simply; there's only one originator at present, so
it's checked in-line in Message's initializer, rather than that iterating through the
available originator modules.
Merge branch 'master' into SNSMessageHandling
revert to ruby 1.8.x hash-syntax

(CI runs tests using ree-1.8.7)
Merge branch 'master' into SNSMessageHandling

* master: (159 commits)
  Fixed an issue with the stubbed responses for S3::Client#complete_multipart_upload.
  Fix undefined method 'version_id' during multipart upload
  Fix bug: default credential provider hides sub credential provider's fetching credentials error.
  missing require time lib for Time.parse is used in EC2Provider, the test passed because there is an example required the time lib
  Bump version to 1.8.1.1
  Removed REE from travis configuration, currently broken on travis-ci.org.
  Removed HTTParty from gem specification.
  Bump version to 1.8.1
  Removed gem dependency on HTTParty.
  Added support for Elastic Transcoding errors and some integration tests.
  Added a basic Elastic Transcoder client.
  Fixed documentation for AWS::CloudFront (incorrect example).
  Fixed "configuraiton" mispelling everywhere
  Spec for allowing workflow_id parameters to some decider methods
  Allow signal_external_workflow_execution and request_cancel_external_workflow_execution to accept a String workflow id as the first parameter. This is consistent with the current documentation.
  Removed @private doc tag from AWS::IAM::Resource.
  Added #create and #create! methods to AWS::Record::AbstractBase
  Removing deprecated usage of nested Given/When/Then from features.
  Removed a few un-needed test dependencies and updated others.
  Fixed spec broken by NetHttpHandler update for network errors.
  ...
Add specs for streaming http responses
Pending specs for more reasonable streaming behaviour

Previously, errors in subsequent chunks were caught and then the whole
request was retried, yielding (possibly) repeated chunks to the
read_block, without any indication (in the block) of this being done.

The outer client method would also not report any errors for a consumer
to check.
Disable retries as soon as any data has been yielded
Merge branch 'SNSMessageHandling' of https://github.com/petemounce/aws-sdk-ruby into petemounce-SNSMessageHandling
AWS::SNS::Message now uses Net::HTTP instead of HTTParty.

HTTParty is no longer a dependency of the SDK.

References #61
Made the pending test for AWS::SNS::Message#authentic? pass.

References #61
Added integration tests for AWS::SNS::Message#authentic?

References #61
Merge pull request #283 from grddev/spec_streaming_http

Spec somewhat reasonable error handling for streaming http responses
Add failover and health check attributes
Don't nuke attributes on ResourceRecordSet update

Previously, if you were not changing the name, type, or set identifier, they
would be destructively removed from the ResourceRecordSet on update.
Resolved an issue with AWS::SNS::Mesage and Ruby versions < 2.0.
AWS::SNS::Message#authentic? no longer flattens errors.

Errors raised when trying to validate the SNS message were
getting replaced with a generic message and a StandardError.
If it fails 3 times, the original error will now raise through.
add AWS.reset_memoization method
Merge pull request #292 from zenazn/nuke

Don't nuke attributes on ResourceRecordSet update
Merge pull request #294 from tongueroo/master

add AWS.reset_memoization method